Xlib can deadlock when using mutlithreaded

Ubuntu version is 8.04 Hardy AMD64

A second machine doesn't really deadlock but recognizes it...
Locking assertion failure. Backtrace:
#0 /usr/lib/libxcb-xlib.so.0 [0x7f23e804097c]
#1 /usr/lib/libxcb-xlib.so.0(xcb_xlib_unlock+0x24) [0x7f23e8040a84]
#2 /usr/lib/libX11.so.6 [0x7f23e8fa0260]
#3 /usr/lib/libX11.so.6(XGetGeometry+0x13b) [0x7f23e8f7e59b]
#4 ./xlibtest(__gxx_personality_v0+0x349) [0x400c71]
#5 /lib/libpthread.so.0 [0x7f23e8d433f7]
#6 /lib/libc.so.6(clone+0x6d) [0x7f23e8318b2d]
Locking assertion failure. Backtrace:
#0 /usr/lib/libxcb-xlib.so.0 [0x7f23e804097c]
#1 /usr/lib/libxcb-xlib.so.0(xcb_xlib_lock+0x15) [0x7f23e8040a15]
#2 /usr/lib/libX11.so.6 [0x7f23e8fa0323]
#3 /usr/lib/libX11.so.6(_XReply+0x14d) [0x7f23e8fa0f8d]
#4 /usr/lib/libX11.so.6(XGetGeometry+0x96) [0x7f23e8f7e4f6]
#5 ./xlibtest(__gxx_personality_v0+0x349) [0x400c71]
#6 /lib/libpthread.so.0 [0x7f23e8d433f7]
#7 /lib/libc.so.6(clone+0x6d) [0x7f23e8318b2d]

On hardy I get the following build error:

bryce@blackwold:~/Desktop$ gcc -g xlibtest.cpp -o xlibtest -lX11 -lpthread
/tmp/ccLdrI4T.o:(.eh_frame+0x12): undefined reference to `__gxx_personality_v0'
collect2: ld returned 1 exit status

.. because it's C++ (e.g. keyword true).
gcc -g xlibtest.cpp -o xlibtest -lX11 -lpthread -lstdc++
or using g++ does compile it.

The locking assertion failure sounds like bug 185311.

Since we're seeing a few issues with traces involving libxcb, I've prepared a non-xcb-enabled libx11 here: http://people.ubuntu.com/~bryce/Testing/libx11/ . (I'm not certain I reverted all the deps correctly, so let me know if there are dependency-related issues with this. You probably should save your old libx11 debs in case the lack of xcb causes problems in other apps.)

I submitted several days ago a bug on freedesktop.org https://bugs.freedesktop.org/show_bug.cgi?id=16617 which consider similar problem. I prepared the simplest test case which
reproduce a problem with libX11 and xcb with multithreaded applications. The problem considers Ubuntu 8.04 LTS which using libXCB.

Maybe Ubuntu should consider releasing officially supported nonxcb libX11 libraries? These problem practically stops using LTS Ubuntu 8.04 with multithreaded X11 applications.

Hi Karol,

We did give consideration to doing this (see https://wiki.ubuntu.com/PlatformTeam/Meetings/20080701), however the issue is that with the noxcb libX11, it breaks compiz in ways that wouldn't be easy to solve. I put a bit more discussion about this onto bug 185311. You're welcome to use this package if it addresses your issue and you don't care about compiz.

Thank you for the test case though! I will forward this to the libxcb developers, and use it as an acceptance test for new libxcb/libx11 releases.

Hello!

I'm very interested in obtaining any information about progress of resolving "xcb" issues in Ubuntu Hardy Heron. Has anybody can simply explain me what is going on or whether anything is going on in ubuntu in this and similar xcb issues?

I saw that Interpid Ibex also have xcb linked with X11 libraries.

Regards,

Currently I'm using testing non-xcb libraries prepared by Bryce with success, but of course compiz not working. (on Hardy Heron).

Hi !

I am interesting in find out more about this deadlock bug, particularly, what is causing the deadlock in libX11.
I can reproduce the bug but the debug info from libX11 is missing so I cannot tell what is the cause of the bug.

Is this bug only due to libX11 code? In this case, is there an associated ticket for libX11?

I am working on a deadlock debugger that tries to reproduce deadlocks and I am particularly interested in reproducing this bug.

Thanks,
Cristi

Some important synchronization was added in libX11 version 1.2. Can this problem be reproduced with that version?

At least my testcase doesn't fail anymore in Jaunty 64bit

ii libx11-dev 2:1.1.99.2-1ubuntu2 X11 client-side library (development headers)
ii libx11-xcb1 2:1.1.99.2-1ubuntu2 Xlib/XCB interface library

I think the original poster's problem should have been solved with the socket-handoff rework in newer libX11/libxcb, such as the versions Norbert most recently reported success with from Jaunty. It isn't obvious to me that Karol's bug or Norbert's locking assertion failure were the same bug as the original post though. Of course the locking assertion failures are no longer detected in socket-handoff versions either, so that problem has disappeared as well.

I did testcase again and on ubuntu 8.04 LTS still hang... But on ubuntu 9.10
(i386, and amd64) seems that is OK and testcase runs correctly.
It consider https://bugs.freedesktop.org/show_bug.cgi?id=16617

I'm closing this as fixed. Backporting the socket-handoff stuff for 8.04 is a no-go, 10.04 is behind the corner anyway..